In the Long Term Evolution (LTE) system or earlier wireless communication systems, a cell may correspond to only one carrier typically with a maximum bandwidth of 20 MHz. In the subsequently proposed Long Term Evolution-Advanced (LTE-A) system, the peak rate of the system has been greatly improved over the LTE system up to 1 Gbps in the downlink and 500 Mbps in the uplink. This requirement can not be satisfied over a carrier with a bandwidth of 20 MHz, and therefore Carrier Aggregation (CA) has been introduced to the LTE-A system so that a plurality of consecutive or inconsecutive carriers in a cell are aggregated together to serve a UE concurrently, where the aggregated carriers are commonly referred to as component carriers, each of which generally has a bandwidth of no more than 20 MHz. As illustrated in FIG. 1, a plurality of (four in the figure) component carriers can be aggregated in an LTE-A cell, and a base station and a UE can transmit data over the aggregated component carriers for an improved throughout of the system.
Scheduling information on resource allocated to UEs is carried over a Physical Downlink Control Channel (PDCCH), and the respective UEs monitor the PDCCH allocated thereto and acquire the resource scheduling information so that they can transmit data only over time and frequency resources indicated by the resource scheduling information. No method for configuring a PDCCH has been proposed so far for the LTE-A system, and if the use of the method for the LTE system were continued, then a UE would have to monitor respective component carriers of the LTE-A system and acquire resource scheduling information over a detected PDCCH, which may mean that the UE has to operate over the respective component carriers and consequently will waste its consumed power.